Automatic refrigerant storage for reversible heat pump



Jan. 31, 1967 w, 5, MCKINNEY 3,301,001

AUTOMATIC REFRIGERANT STORAGE FOR REVERSIBLE HEAT PUMP Filed Nov. 5, 1965 A 2 Sheets$heet 1 INVENTOR W/LL/AM SMCKl/V/VEY Jan. 31, 1967 w, s, MCKINNEY 3,301,001

AUTOMATIC REFRIGERANT STORAGE FOR REVERSIBLE HEAT PUMP Filed Nov. 5, 1965 2 Sheets-Sheet 2 IN VEN TOR 19W, m M WW United States Patent 3,301,001 AUTOMATIC REFRIGERANT STORAGE FOR REVERSIBLE HEAT PUMP William S. McKinney, Huntington Beach. Calif., assignor to The Coleman Company, Inc, Wichita, Kans., a corporation of Kansas Filed Nov. 5, 1965, Ser. No. 506,553 6 Claims. (Cl. 62149) This invention relates to an automatic refrigerant storage for a reversible heat pump, and more specifically, to a reversible heat pump with improved means for adjusting the effective charge of refrigerant.

It has been previously observed, in Hopkins Patent 2,589,384, that in any commercially useful reversible heat pump, the refrigerant charge which is correct for one direction of flow is wrong for the other direction. Hopkins, therefore, teaches the interposition of a refrigerant storage tank in the circuit of the heat pump, such tank being disposed adjacent the heat exchanger which operates as a condenser when the larger charge is needed, and being connected by a tube with a part of the circuit which is at the pressure of the other heat exchanger.

In practice, it has been found that such a storage tank provides, at best, only a partial solution to the problem. While the storage tank does have the effect of automatically adjusting the charge, it also produces, or cooperates with the other components of the system to produce, certain undesirable side effects. For example, in a heat pump which requires a larger charge during the cooling cycle, a change-over from heating to cooling will cause refrigerant to surge from the storage tank located adjacent the outdoor coil (which acts as a condenser during the cooling cycle) and into the system. Rapid emptying of the storage tank may cause flooding of the evaporator coil and, if liquid refrigerant then continues on the compressor, the oil of the compressor will be diluted and the slug of liquid refrigerant entering the compressor may even damage the valves.

Ordinarily, heat pump systems require a greater charge during the cooling cycle. The storage tank thus removes excess charge on the heating cycle to give optimum capacity to the heatpump; however, such optimum capacities are usually based on conditions which will exist during mild outdoor temperatures. As outdoor temperatures fall below this predetermined level, the outdoor coil, which acts as an evaporatorduring the heating cycle, receives less and less heat from the air and, if a sufficiently low outdoor temperature is reached, liquid refrigerant will be drawn into the compressor, again reducing the viscosity of the oil to a point which may cause compressor breakdown.

Accordingly, it is an" object of the present invention to provide a reversible heat pump in which the charge is automatically adjusted to suit the particular cycle of operation, without the dangers and disadvantages described above. Specifically, it is an object to provide a heat pump equipped not only with a storage tank for withdrawing excess refrigerant from the system during certain conditions of operation, but also with additional storage means which coacts with the tank for automatically controlling the charge and for eliminating or reducing those operating conditions which might otherwise result in compressor breakdown.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a generally diagrammatic view of a heat pump circuit illustrating the direction of refrigerant flow when the heat pump is in its cooling cycle of operation.

FIGURE 2 is a diagrammatic view similar to FIGURE 1 and showing the heat pump during its cooling cycle, but

other direction.

veyed to the compressor.

3,301,001 Patented Jan. 31, 1967 'ice under conditions where there is a high internal load on the system.

FIGURE 3 is a diagrammatic view similar to FIGURE 1 but illustrating the operation of the system when the heat pump is in its heating cycle of operation.

FIGURE 4 is similar to FIGURE 3, showing the heat pump during its heating cycle of operation, but under conditions where the outside temperature is extremely low.

As previously indicated, it is a characteristic of reversible heat pumps that a refrigerant charge which is correct for one direction of operation is wrong for the Normally, a larger charge is needed .during the cooling cycle and, therefore, excess charge must be removed during the heating cycle. The accompanying drawings refer to such a system; that is, a system in which excess charge must be removed during the heating cycle, and must be returned to the system during the cooling cycle, in order to maintain optimum operating conditions. It will be understood as the specification proceeds, however, that the teachings of the present invention are also applicable to a heat pump in which the larger vcharge is required during the heating cycle and the smaller one during the cooling cycle.

The heat pump diagrammatically illustrated in FIG- URE 1 comprises two coil heat exchangers 10 and 11, a motor-driven compressor 12, a 4-way reversing valve 13, and a capillary tube arrangement 14, which operates as a long-path restrictor.

Between reversing valve 13 and compressor 14 is a suction line 15 through which refrigerant vapor is con- A discharge line 16 extends from the compressor back to the reversing valve and carries refrigerant under pressure to the valve and to the particular coil 10 or 11 which has been selected to operate as the condenser.

The capillary tube arrangement 14 includes capillary tubes 17 and 18, the former being operative during the heating cycle and the latter being operative during the cooling cycle. Lines 19 and 20, each equipped with a check valve 21 and 22, direct the flow of refrigerant to the capillary tubes. During a cooling cycle, when the refrigerant flows in the direction indicated by arrows 23, line 19 is operative to convey refrigerant from the outdoor coil 10, which operates as a condenser, to capillary tube 18. The flow of refrigerant from line 10 through line 20 is blocked by check valve 22. On the other hand, when the flow of refrigerant is reversed during the cooling cycle, as indicated by arrows 2 1- in FIGURE 3, refrigerant flows from the indoor coil 11, which then operates as the condenser, through line 20 and through capillary tube 17. Under such conditions, the flow of refrigerant through line 19 is blocked by check valve 21.

A conventional drier 249a may be interposed in the line leading to the capillary tubes to withdraw any moisture from the refrigerant charge. To avoid chemical breakdown of the refrigerant, it is desirable to maintain the moisture level below forty parts water per one million parts refrigerant.

All of the parts of the closed system so far described are entirely conventional. Since such components, including the drier 25, capillary tubes 17 and 18, compressor 12, reversing valve 13, and coils 10 and 11, are well known components of heat pumps, a further description of their structure is believed unnecessary herein.

Adjacent coil 11, which operates as a condenser when the smaller refrigerant charge is required, is a storage tank 25. The refrigerant storage tank is completely sealed except for a single line 26 which enters the bottom of the tank and which communicates with refrigerant line 20 between coil 11 and check valve 22. It is important that the storage tank 25 be adjacent to, but spaced from, coil 11. If the tank is mechanically or physically connected to the coil, then the tank walls would tend to assume the same temperature as the coil itself, resulting in improper operation of the system. Heat transfer between the storage tank and the adjacent coil 11 must be avoided; however, the tank should be positioned close enough to the coil so that its walls will react to the temperature of the air either entering or leaving the coil 11.

Interposed along suction line 15 is a vertically-elongated accumulator tank 27. Portion 15a of line 15 communicates with an opening at the upper end of the accumulator tank and serves as the inlet line therefor. Portion 15b, Which extends to the compressor 12, also communicates with a second opening at the upper end of accumulator tank 27 and serves as a discharge line for that tank.

The volume of the accumulator tank is critical. Its capacity must not exceed the volume of oil which the compressor 12 might lose before reaching its lowest operating oil level. In other words, the volume of the accumulator tank must be less than the difference between the maximum and minimum operating oil capacities of the compressor. In practice, it has been found that the accumulator tank capacity should be substantially less than this difference because, in normal operation of the compressor, some oil necessarily circulates through the refrigerant system.

The capacities of the storage tank 25 and accumulator tank 27 are closely related. Specifically, the combined capacities of the storage and accumulator tanks should equal the volume of excess charge which must be removed from the refrigerant system during one of its cycles of operation. Normally, as previously indicated, excess charge must be removed during the heating cycle; therefore, the combined capacities of the accumulator and storage tanks should equal the excess charge which must be removed from circulation through the system in order to achieve the optimum charge when the apparatus is operating at the lowest ambient (outside) temperature to which the outdoor coil is expected to be subjected.

Broken line 28 indicates the physical disposition of the various components when the heat pump is installed for operation. All of the components disposed to the left of line 28 are normally positioned outside of an inclosure and are subjected to outdoor temperatures, whereas those components to the right of line 28 are normally located within an inclosure and are subjected to indoor temperatures.

FIGURES 1 and 2 illustrate the heat pump during a cooling cycle when it operates as an air conditioner. Coil 11 serves as an evaporator, withdrawing heat from the room air space. The vaporized refrigerant is drawn through suction 15 into compressor 12 and is then pumped under pressure to the outdoor coil 11 which serves as a condenser. Storage tank 25 remains empty, since the temperature of its walls remain Well above the condensation temperature of the refrigerant and any refrlgerant flowing therein through line 26 would quickly boil off. Refrigerant flows into and out of accumulator 27 on its way to compressor 12.

FIGURE 2 illustrates the condition which results during a cooling cycle when the gas returning from the evaporator to the compressor is superheated. Oil, flowing along with the superheated gas, collects in the accumulator. Once the system shuts off or catches up with the load, the oil in the accumulator tank will boil off with liquid refrigerant and return to the compressor. As previously indicated, the capacity of the accumulator must be limited to the volume of oil that can be removed from the system without impairing operation of the compressor.

During a heating cycle (FIGURES 3 and 4) the indoor coil 11 operates as a condenser and the outdoor coil operates as an evaporator. The flow of refrigerant through the circuit is reversed and, since the storage tank 25 taps into the circuit adjacent the condenser, it

collects liquid refrigerant flowing from the condenser. In effect, the storage tank removes from the system that portion of the refrigerant charge which is in excess of the optimum charge required for operation of the heat pump under moderate outdoor temperature conditions. Gaseous refrigerant flows from the evaporator through reversing valve 13 and suction line 15 into compressor 12. Since the returning refrigerant is in a gaseous state during such moderate outdoor temperature conditions, it simply flows into and out of the accumulator tank on its way to the compressor.

As the outdoor temperature drops, coil 10, which acts as an evaporator on the heating cycle, receives decreasing amounts of heat from the air. Under extremely low outdoor temperature conditions, the amount of heat available to the outdoor coil is insufficient to vaporize all the refrigerant and liquid refrigerant therefore flows from the outdoor coil towards compressor 12. However, under such conditions, the accumulator tank 27 operates as an auxiliary storage tank to collect liquid refrigerant and thereby further reduce the charge of refrigerant in the system (FIGURE 4). Liquid refrigerant which might otherwise pass into the compressor to dilute the oil to the point where im lubricating effectiveness is destroyed is thereby avoided. The storage tank 25 and accumulator tank 27 thereby coact to withdraw excess charge from the system during the lowest outdoor temperatures at which the heat pump is expected to operate. The combined capacities of the storage tank and accumulator are such that at very low outdoor temperatures, when flooding of the evaporator coil occurs, there is not enough refrigerant left in the system to dilute the viscosity of the oil enough to damage the compressor.

It will be observed that storage tank 25 is disposed in the air stream of the coil 11 with which it communicates. It has been found that if the storage tank is instead placed in the air stream of the other coil 10 (while retaining its flow of communication with coil 11) serious oil Washout may occur and may cause compressor failure, under certain operating conditions. This problem is avoided by locating storage tank 25 adjacent the coil with which it communicates; that is, the coil which operates as a condenser when the smaller refrigerant charge is required.

If the storage tank were instead located adjacent the outdoor coil, while retaining its How of communication with the indoor coil, and the system were accidently adjusted into a heating cycle during high summer temperatures, then the storage tank would be filled and the indoor coil would act as a condenser. If the cycle were then reversed, either accidently or intentionally, the storage tank, which would be exposed to hot outdoor conditions, would empty rapidly, far more rapidly than if it were located as shown adjacent the indoor coil. Liquid refrigerant discharged from the rapidly-emptying storage tank would flow through the outdoor coil and surge into the compressor, causing oil washout and, possibly, compressor failure.

This problem is avoided by locating the storage tank adjacent the coil to which it is connected. Should the same conditions of operation described above accidently or intentionally take place, the storage tank will empty more slowly and, even if a slug of liquid refrigerant should pass from the evaporator coil towards the compressor, it will be collected in accumulator 27. Relatively slow emptying and filling of the storage tank 25, which results from the location of that tank adjacent coil 11, also has the further advantage of reducing the operating noise level of the system as a whole.

Should the system be such that a larger charge is required during the heating cycle, it is to be understood that the storage tank 25 should again be located adjacent to, and in communication with, the coil which operates as a condenser when the smaller charge is needed; in that case, coil 10. In other respects, the structure and operation would be identical to that already described.

r 5 The combined capacities of storage tank 25 and accumulator tank 27 would be equal to the excess charge which must be removed from the system when the indoor temperature is at its lowest practical or expected level.

While in the foregoing I have disclosed an embodiment of the invention in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

I claim:

1. A reversible heat pump circuit comprising a first heat exchanger capable of operating selectively as a condenser or as an evaporator; 21 second heat exchanger capable of operating selectively as an evaporator; a second heat exchanger capable of operating selectively as an evaporator or as a condenser; a flow resistor connecting said first and second heat exchanger for the reversible flow of refrigerant therethrough, a compressor interposed between said exchangers and completing the circuit, reversing means in said circuit for selectively reversing the direction of flow from said compressor to and from said heat exchangers, the thermal characteristics of the circuit being such that one of the directions requires for eflicient operation an effective charge larger than the charge for the other of said directions, a quantity of refrigerant in the circuit corresponding with the larger charge, a refrigerant storage tank equipped with a twoway flow connector which communicates with the circuit between said exchangers and adjacent to the exchanger which operates as a condenser when the smaller charge is needed, and an accumulator tank communicating with the circuits at a point along the compressors refrigerant intake line, the capacity of said accumulator tank being no greater than the volume of oil which may be withdrawn from the compressor without impairing compressor operation, and the combined capacities of said accumulator and storage tanks being equal to the volume of excess charge present when the flow of refrigerant in said circuit is in said other direction so that a smaller refrigerant charge is needed, and the heat exchanger which then operates as an evaporator is subjected to its lowest expected ambient temperatures.

2. The structure of claim 1 in which said storage tank is disposed adjacent the heat exchanger which operates as a condenser when the smaller refrigerant charge is needed.

3. The structure of claim 1 in which said accumulator tank has inlet and outlet openings communicating with said circuit; said accumulator tank being vertically elongated and said openings being located adjacent to the upper end thereof.

4. A reversible heat pump circuit comprising a first heat exchanger capable of operating selectively as a condenser or as an evaporator, a second heat exchanger capable of operating selectively as an evaporator or as a condenser; a fiow restrictor connecting said first and second heat exchangers 'for the reversible flow of refrigerant therethrough; a compressor interposed between said exchangers and completing the circuit; reversing means in said circuit for selectively reversing the direction of flow from said compressor to and from said heat exchangers; the thermal characteristics of the circuit being such that a larger charge is required during a cooling cycle when said first exchanger operates as a condenser and said second exchanger operates as an evaporator, and a smaller charge is required during a heating cycle when said first exchanger operates as an evaporator and said second exchanger operates as a condenser; a quantity of refrigerant in the circuit corresponding with the larger charge; a refrigerant storage tank equipped with a two-way flow connector which communicates with the circuit adjacent said second heat exchanger; and an accumulator tank communicating with the circuit at a point along the compressors refrigerant intake line; the capacity of said accumulator tank being no greater than the volume of oil which may be withdrawn from the compressor Without impairing compressor operation; and the combined capacities of said accumulator and storage tanks being equal to the volume of the excess charge present during a heating cycle when said first heat exchanger is subjected to its lowest expected ambient temperatures.

5. The structure of claim 4 in which said storage tank is spaced closely to said second heat exchanger.

6. The structure of claim 4 in which said accumulator tank has inlet and outlet openings located adjacent the upper end thereof.

References Cited by the Examiner UNITED STATES PATENTS 2,589,384 3/1952 Hopkins 62160 2,715,317 8/1955 Rhodes 62149 2,969,655 1/1961 Salter 62174 3,006,155 10/1961 Vanderlee 62149 3,065,610 11/1962 Maudlin 62-149 3,237,422 3/1966 Pugh 62149 WILLIAM J. WYE, Primary Examiner. 

1. A REVERSIBLE HEAT PUMP CIRCUIT COMPRISING A FIRST HEAT EXCHANGER CAPABLE OF OPERATING SELECTIVELY AS A CONDENSER OR AS AN EVAPORATOR; A SECOND HEAT EXCHANGER CAPABLE OF OPERATING SELECTIVELY AS AN EVAPORATOR; A SECOND HEAT EXCHANGER CAPABLE OF OPERATING SELECTIVELY AS AN EVAPORATOR OR AS A CONDENSER; A FLOW RESISTOR CONNECTING SAID FIRST AND SECOND HEAT EXCHANGER FOR THE REVERSIBLE FLOW OF REFRIGERANT THERETHROUGH, A COMPRESSOR INTERPOSED BETWEEN SAID EXCHANGERS AND COMPLETING THE CIRCUIT, REVERSING MEANS IN SAID CIRCUIT FOR SELECTIVELY REVERSING THE DIRECTION OF FLOW FROM SAID COMPRESSOR TO AND FROM SAID HEAT EXCHANGERS, THE THERMAL CHARACTERISTICS OF THE CIRCUIT BEING SUCH THAT ONE OF THE DIRECTIONS REQUIRES FOR EFFICIENT OPERATION AN EFFECTIVE CHARGE LARGER THAN THE CHARGE FOR THE OTHER OF SAID DIRECTIONS, A QUANTITY OF REFRIGERANT IN THE CIRCUIT CORRESPONDING WITH THE LARGER CHARGE, A REFRIGERANT STORAGE TANK EQUIPPED WITH A TWOWAY FLOW CONNECTOR WHICH COMMUNICATES WITH THE CIRCUIT BETWEEN SAID EXCHANGERS AND ADJACENT TO THE EXCHANGER WHICH OPERATES AS A CONDENSER WHEN THE SMALLER CHARGE IS NEEDED, AND A ACCUMULATOR TANK COMMUNICATING WITH THE CIRCUITS AT A POINT ALONG THE COMPRESSOR''S REFRIGERANT INTAKE LINE, THE CAPACITY OF SAID ACCUMULATOR TANK BEING NO GREATER THAN THE VOLUME OF OIL WHICH MAY BE WITHDRAWN FROM THE COMPRESSOR WITHOUT IMPAIRING COMPRESSOR OPERATION, AND THE COMBINED CAPACITIES OF SAID ACCUMULATOR AND STORAGE TANKS BEING EQUAL TO THE VOLUME OF EXCESS CHARGE PRESENT WHEN THE FLOW OF REFRIGERANT IN SAID CIRCUIT IS IN SAID OTHER DIRECTION SO THAT A SMALLER REFRIGERANT CHARGE IS NEEDED, AND THE HEAT EXCHANGER WHICH THEN OPERATES AS AN EVAPORATOR IS SUBJECTED TO ITS LOWEST EXPECTED AMBIENT TEMPERATURES. 